Searching for reservoirs with bypassed oil using well tests and mathematical modeling

Abstract

The increase of oil recovery by the involvement of bypassed oil into production is a significant source of oil production increase at a minimal cost. Bypassed oil zones identification possibilities researched through mathematical flow modeling and simulated well tests. Two hypothetical models of homogeneous and heterogeneous (with low permeability zones) oil formations were generated, in which the bypassed oil was trapped during the production. Based on these models, the authors calculated data of comprehensive well tests: buildup, drawdown and interference. The aspects of the well test interpretation results data obtained for both models through the best-match method allowed bypassed oil areas identification possibility assessment. A significant difference between the cumulative oil rate actually observed at the field and the one obtained in the model is the first diagnostic feature, which suggests the presence of bypassed oil. During the pressure buildup (drawdown) tests, the curves of pressure change derivatives on the Bourdet diagnostic plots for heterogeneous and homogeneous models differ significantly, which is the second diagnostic feature that suggests the presence of bypassed oil. The analysis of the data processing results obtained during the pressure buildup tests indicated cases of significant changes in conductivity over time which is associated with higher water cut due to the absence of any obstacles for water to flow through. This factor can be considered a third diagnostic feature. During the interference tests of a heterogeneous model in multiple directions, the permeability of the interwell space in all directions turned out to be much lower in comparison to the reservoir permeability in the vicinity of the wells, that is explained by the bypassed oil presence — this is the fourth diagnostic feature which suggests the bypassed oil presence in the interwell space. The obtained results of well test data interpretation means a possibility to identify undeveloped areas with bypassed oil, filtration model improvement and recommendations development of infill drilling or sidetracks for the residual reserves extraction. • The comprehensive well tests allows bypassed oil areas identification. • The presence of bypassed oil have an influence on Bourdet diagnostic plots at different time of production history. • The occurrence of bypassed oil cause obstacles for water to flow and slow down the change in conductivity. • The decrease of permeability according to the interference test results indicates the presence of bypassed oil.